This invention relates to a film advance mechanism for cameras which use separate, card-like film units. Film of this type is presently used in cameras of the self-developing type and accordingly, for clarity of description, the invention is described with principal reference to such cameras.
More particularly, the invention provides a film advance mechanism for cameras that use a film assemblage in the form of a cassette which houses a stack of separate card-like film units. This type of film cassette is commercially available from Polaroid Corporation in Cambridge, Massachusetts, for use in cameras sold under the registered designations SX-70 and PRONTO!, and is described in U.S. Pat. No. 3,651,746 of E. H. Land entitled "Film Assemblage". The film units in the cassette, disclosed in U.S. Pat. No. 3,415,644 of E. H. Land for "Novel Photographic Products And Processes", are stacked with a foremost one available for photographic exposure through an exposure window.
The case of the film cassette has an exit slot in a forward end wall and a flange-bordered exposure window in an upper wall. An access slot in the upper flange extends forward for a short distance from the rear end wall. This slot provides access for a movable pick member to engage an exposed film unit and advance it out of the cassette through the exit slot.
Cameras suitable for use with film assemblages of this type are described in U.S. Pat. No. 3,753,392 of E. H. Land entitled "Film-Advancing Apparatus", and in U.S. Patent application Ser. No. 648,725 of Johnson et al filed Jan. 13, 1976 for "Shutter Latch Arrangement Releasable Through Shutter Blade Actuation And Resettable Through Film Advancement", and assigned to the assignee hereof. Each of these cameras has film advancing apparatus which indexes an exposed film unit out of the cassette and feeds it to processing elements, typically a pair of spread rollers. The apparatus includes the pick member which enters the above-mentioned access slot of the cassette and engages the rear edge of the foremost film unit. The pick member is driven, typically by a motor, along the length of the access slot to advance the film unit by a distance essentially equal to, but limited by, the slot length.
Each camera also includes a pair of rollers, at least one of which is driven, positioned to receive the leading edge of a film unit that has been advanced in the foregoing manner, i.e., by a distance equal to the length of the cassette access slot. The roller pair ruptures a pod of photoprocessing fluid in the film unit and spreads the fluid over an internal layer to initiate development of the latent image on the film unit. In this process, the rollers draw the film unit out of the cassette and discharge it from the camera. The spread rollers are spaced from the cassette by a short distance limited by the length of the cassette access slot. This constraint, which the length of the cassette slot imposes on the placement of the rollers, imposes constraints on other design features of the camera, including the overall arrangement of the camera elements, the arrangement and nature of the optical system, and the arrangement of internal mechanisms such as the mechanism which drives the rollers.
In view of the above discussion, it is a principal object of the invention to provide a camera mechanism for advancing separate, card-like and cassette-housed film units, and which provides a greater magnitude of film advance than heretofore available.
It is also an object of the invention to provide a film advance mechanism of the above character which can advance a card-like film unit from within a cassette having an access opening for pick-indexing of the foremost card unit, and which provides advance over a distance significantly greater than the length of that access opening.
A more particular object of the invention is to provide a film advance mechanism of the above character for a self-developing camera and which provides a relatively long span of film advance from within the film cassette to the processing-initiating spread rollers.
Another object of the invention is to provide a film advance mechanism of the above character which provides a greater magnitude of film advance by engagement with the back edge of a cassette-housed film unit than heretofore available.
It is a further object of the invention to provide a film advance mechanism having the foregoing features and which is relatively inexpensive to manufacture, which is compact, and which is highly reliable in operation so as to be essentially fool-proof.
Other objects of the invention will in part be obvious and will in part appear hereinafter.